Multiplayer server not responding

So me and a friend are trying to paly together so weve both tried making the server and when the other tries joining it just states “Server not responding” even though we can see each other playing across the room how do we fix this?

/bump

Need to forward ports

which ones? i forwarded a couple but im not sure which ones i need to allow my friedns to connect to me?

http://www.facepunch.com/showthread.php?t=817853